Field of the Invention
Transposons, or transposable elements, are mobile genetic elements characterized by their ability to move in and out of their host genome in a manner similar to bacteriophages. However, unlike bacteriophages, transposable elements are unable to move from host to host, since they lack the structural features necessary to package and deliver the nucleic acid.
Transposable elements have been shown to induce recombination in yeast (Boeke, ed. Berg & Howe, Mobile DNA 335 (Am. Soc. Microbio. 1989); drosophila (Davis et al., 84 PNAS 174 (1987) and Busseau et al., 218 Mol. Gen. Genet. 222 (1989)) and plants (Martin et al., 119 Genetics 171 (1988), McClintock, 53 Washington Year Book 254 (1954), Doring et al., 184 Mol. Gen. Genet. 377 (1981), Taylor and Walbot, 4 EMBO J. (1985), Dooner et al., 211 Mol. Gen. Genet. 485 (1988); Lowe et al., 132 Genetics 813 (1992) and Athma and Peterson, 128 Genetics 163 (1991)). The recombinations resulted in deletions, duplications and other rearrangements. These studies were limited to observations of natural phenomenon in the organisms, and did not involve in situ recombination of non-self constructs.
Human manipulation of transposons has been limited, until the present invention, to insertion and excision of transposons, with or without accompanying nucleic acid. For example, U.S. Pat. No. 5,482,852 to Yoder et al. describes a technique for inserting an expression-cassette-containing transposon into plant cells, selecting cells which contain the transposon, and subsequently crossing the plant so as to remove the transposon sequences, but not the expression cassette. U.S. Pat. No. 5,013,658 to Dooner describes a method to use selectable markers in transposons as tags for genetic studies. U.S. Pat. No. 5,478,369 to Albertson describes a male-fertility mediating gene which was cloned through the use of the Ac (maize) transposon.
Human manipulation of recombination has been limited, until the present invention, to non-transposon related methods. U.S. Pat. No. 5,527,695 to Hodges et al. describes the use of a recombinase enzyme to induce recombination in situ of a construct with homologous direct repeats. U.S. Pat. No. 5,658,772 to Odell et al. describes a similar method, but the crossover site and the recombinase enzyme are more defined (lox and Cre, respectively). In Arabidopsis, generation of double strand breaks by HO endonuclease increased the frequency of somatic intrachromasomal homologous recombination by about 10 fold. Chiurazzi et al., 8 Plant Cell 2057 (1996). Moreover, double strand breaks are known to initiate recombination in fungi. Szostak et al., 33 Cell 25 (1983).
Citation of the above documents is not intended as an admission that any of the foregoing is pertinent prior art. All statements as to the date or representation as to the contents of these documents is based on subjective characterization of information available to the applicant at the time of writing, and does not constitute an admission as to the accuracy of the dates or contents of these documents.